This invention relates to cation-exchange materials and methods for forming the same and more particularly relates to cation-exchange support materials that are particularly well suited as packing materials for liquid chromatography.
High-performance anion and cation-exchange chromatography have become powerful tools for the analysis and isolation of biological molecules. Cation-exchange coatings for high performance liquid chromatography media have been synthesized by several routes. The simplest route is the silylation of a silica surface with an anionic organosilane. However, such reactions are reversible and can leave residual silanols which can irreversibly blind protein. Although this problem can be circumvented by bonding a hydrophilic organic polymer layer over the silica surface, this procedure does not give the required reproducibility. Another route for the synthesis of a cation-exchange coating is to start with an organosilane reaction to place a reactive function on a silica surface. The functionalized silica is then reacted with a preformed polymer providing a covalently bonded polymeric stationary phase. The last step further modifies the anchored polymer so that it is anionic. Although the cation-exchange coating produced is stable and of high binding capacity, this method for preparing cation-exchange coatings is quite lengthy.
Previous work by Alpert and Regnier with adsorbed polyethyleneimine chemistry as discussed in U.S. Pat. No. 4,245,005, the teachings of which are incorporated herein by reference, has shown it to be extremely versatile for the synthesis of anion-exchange stationary phases. Utilizing the existing adsorption technology pioneered by Alpert and Regnier for the synthesis of adsorbed polymeric anion-exchange media, cation-exchange materials of the invention have been produced.
European patent application No. 0 143 423 teaches cation-exchange matrials produced from polyethyleneimine; however, European patent application No. 0 143 423 provides a porous silica to which a non-crosslinked polyethyleneiminopropyl silane is covalently bonded, rather than adsorbed. In European patent application No. 0 143 423, particulate silica gel is reacted with polyethyleniminopropyl trimethoxy silane and the non-crosslinked covalently bonded polyethyleniminopropylsilyl-silica may be converted to a weakly acidic carboxylated form by conventional treatment, for example, with an appropriate dibasic acid anhydride in an inert organic solvent.